code: def test_histogram(start_prometheus_http_server):
      h = Histogram("test_histogram")
      assert h.name == "test_histogram"
      assert h.description == ""
      assert set(["host", "pid"]).issubset(set(h.tag_keys))
      assert h.type == "Histogram"
      num = 3
      while num > 0:
          h.record(1)
          h.record(2)
          time.sleep(1)
          num -= 1
      verify_metric("test_histogram", 1.5, 0.15)
      num = 3
      while num > 0:
          h.record(3)
          time.sleep(1)
          num -= 1
      verify_metric("test_histogram", 3, 0.1)
  
file_path: mars/mars/metrics/backends/prometheus/tests/test_prometheus_metric.py
imports: import pytest
  import time
  from .....utils import get_next_port
  from ..prometheus_metric import Counter, Gauge, Histogram, Meter
label_desc: Use image node_id 6 for calling a global function with example usage: test_histogram(start_prometheus_http_server) without return types